Convertible downhole isolation plug

ABSTRACT

A downhole tool that is capable of isolating communication pressure from below the set downhole tool, and is capable of being converted to a frac plug is provided. The downhole tool includes a packer with a ball seat defined therein. A plug is disposed at a lower end of the downhole tool to isolate the upper well from the lower well. A sealing ball is carried with the packer into the well by a setting tool. The movement of the sealing ball away from the ball seat is limited by isolation of the sealing ball from the lower well. A rod is disposed through the downhole tool contacting the plug. The rod is partially disposed in the ball seat, preventing the sealing ball from sealing. When the packer is set, flow within the well is isolated, thereby allowing treatment of the well above the packer. With the application of sufficient pressure, the sealing ball applies force to the rod which shears the plug from within the tool. The tool is converted to a standard frac plug.

This disclosure relates to downhole tools for use in oil and gaswellbores and to methods for treating wellbores. This disclosureparticularly relates to downhole packers that are convertible from abridge plug to a frac plug without removing the packer from thewellbore.

In the drilling or reworking of oil wells, numerous varieties ofdownhole tools are used. For example, but not by way of limitation, itis often desirable to seal tubing or other pipe in a well casing when itis desired to pump cement or other slurry down the tubing and force theslurry out into a formation. Thus, it becomes necessary to seal thetubing with respect to the well casing, and to prevent the fluidpressure of the slurry from lifting the tubing out of the well. Downholetools, referred to as packers and bridge plugs, are designed to providefor the ability to seal tubing or other pipe in the well casing, and arewell known in the art of producing oil and gas.

Packers and bridge plugs typically make use of metallic or non-metallicslip elements, or slips. The slips are initially retained in closeproximity to the mandrel, but are subsequently forced outwardly awayfrom the mandrel to engage a casing that was previously installed withinthe wellbore. Thus, when the tool is positioned at the desired depth,the slips are forced outward against the wellbore to secure the packer,or bridge plug, so the tool will not move relative to the casing duringoperations. Some non-limiting example operations include testing,stimulating production of the well, or plugging all or a portion of thewell.

One problem encountered by well operators using packers and bridge plugsis that the packer and/or plug must be removed prior to the installationof other types of plugs. A frac plug is a good example. A frac plug isessentially a downhole packer with a ball seat for receiving a sealingball. When the packer is set and the sealing ball engages the ball seat,the casing, or other pipe in which the frac plug is set, is sealed. Oncethe sealing ball is set, the operator is able to pump fluid into thewell, and pumped fluid may be forced into a formation above the fracplug. Often, it is necessary to completely block flow from a lower zoneto facilitate treatment of an upper zone, or conduct some other processin the upper zone. After the initial treatment or other process iscomplete, it may be desirable to allow flow from the lower zone, and tobe able to restrict that flow. There is a need for tools that can be setin the well to act as a bridge plug, and can be converted to a frac plugwhile in the well.

SUMMARY

One disclosed embodiment is a downhole tool for use in a well. Thedownhole tool comprises a mandrel defining a central flow passagetherethrough and a ball seat thereon. A sealing element is disposedabout the mandrel. The downhole tool is movable from an unset to a setposition in the well in which the sealing element engages the well. Asolid plug for blocking flow through the downhole tool is removablyconnected in the mandrel. A sealing ball is positioned in the well andis longitudinally spaced from the ball seat. The application of apredetermined pressure in the well will simultaneously remove the solidplug and move the sealing ball into engagement with the ball seat.

Another embodiment provides a downhole tool for use in a well. Thedownhole tool comprises a mandrel having an upper and a lower end. Themandrel defines a longitudinal central flow passage therethrough. Themandrel also defines a ball seat on the upper end thereof. A sealingelement is disposed about the mandrel for sealingly engaging the well. Aplug is detachably retained within the mandrel and a rod is disposedwithin the longitudinal central flow passage. The rod has a first endcontacting the plug, and a second end contacting a sealing ball to spacethe sealing ball from the ball seat.

Another embodiment provides a method for converting a downhole toolpositioned in a well from a bridge plug to a frac plug. The methodcomprises lowering the downhole tool into the well. The downhole tooldefines a longitudinal central flow passage therethrough. The methodfurther includes the step of setting the downhole tool in the well,where the downhole tool engages the well. Flow through the tool isblocked in both an upward and a downward direction through thelongitudinal central flow passage with a solid plug detachably connectedto the tool. A sealing ball is positioned in the well above thelongitudinal central flow passage. Pressure is increased in the well,thereby causing the solid plug to detach from the downhole tool and movethe sealing ball into engagement with a ball seat that is positioned onthe downhole tool. When the sealing ball is in engagement with the ballseat, downward flow through the downhole tool is prevented but upwardflow therethrough is permitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows two downhole tools positioned in a well.

FIG. 2 is a cross-sectional view of the downhole tool in an unsetposition.

FIG. 3 is a cross-sectional view of the downhole tool in a set position.

FIG. 4 is a cross-sectional view of the downhole tool with the plugdetached.

DETAILED DESCRIPTION

In the description that follows, similar parts are marked throughout thespecification and drawings with the same reference numerals,respectively. The drawings are not necessarily to scale, and theproportions of certain parts have been exaggerated to better illustratedetails and features of the invention. In the following description, theterms “upper,” “upward,” “lower,” “below,” “downhole” and the like asused herein shall mean in relation to the bottom or furthest extent ofthe surrounding wellbore. This applies even though the well or portionsof it may be deviated or horizontal. The terms “inwardly” and“outwardly” are directions toward and away from, respectively, thegeometric center of a referenced object. Where components of relativelywell-known designs are employed, their structure and operation will notbe described in detail.

Referring to the drawings, and in particular FIG. 1, the downhole toolof the present invention is shown and designated by the numeral 10.Downhole tool 10 has an upper end 11 and a lower end 13. In FIG. 1, twodownhole tools 10 are shown, and may be referred to herein as lowerdownhole tool 10 a and second or upper downhole tool 10 b. Downholetools 10 a and 10 b may be identical, and the subscripts a and b areused to designate simply that the tools are at different positions inthe well.

FIG. 1 schematically depicts downhole tools 10 in set positions in well14, which is comprised of wellbore 12 with a casing 16 cemented therein.Well 14 may intersect one or more formations or zones, such as firstzone 18 and second zone 20. Downhole tools 10 are shown after beinglowered into well 14 with a setting tool 22. Setting tool 22 may be anytype known in the art. One example of setting tool 22 is depicted inFIG. 2.

Referring to FIG. 2, a cross-section of downhole tool 10 is shown withsetting tool 22 attached thereto for running downhole tool 10 into well14. Downhole tool 10 is in an unset position in FIG. 2. Downhole tool 10is commonly referred to as a packer, and herein is referred to as packer24. Packer 24 comprises mandrel 26 with first, or upper end 28, andsecond, or lower end 30. Mandrel 26 defines longitudinal central flowpassage 32 to allow fluid communication therethrough. Mandrel 26 definesball seat 34 on the upper end 28 thereof. Ball seat 34 has a lower end33 positioned where ball seat 34 flows into longitudinal central flowpassage 32. Sealing ball 35 is positioned between setting tool 22 andball seat 34 and is spaced from ball seat 34. Sealing ball 35 may bereferred to as frac ball 35.

Packer 24 is designed to be set in well 14. Thus, mandrel 26 has sealingelement 36 disposed thereabout. A spacer ring 38 is secured to mandrel26 with pins 40. Spacer ring 38 provides an abutment which serves toaxially retain slip segments 42, which are positioned circumferentiallyabout mandrel 26. Slip segments 42 may utilize ceramic buttons 44 asdescribed in detail in U.S. Pat. No. 5,984,007, which is incorporated byreference herein. Slip retaining bands 46 serve to radially retain slipsegments 42 in an initial circumferential position about mandrel 26.Slip retaining bands 46 may be made of a steel wire, a plastic material,or a composite material having the requisite characteristics ofsufficient strength to hold the slip segments 42 in place prior tosetting downhole tool 10, and are drillable. Preferably, slip retainingbands 46 are inexpensive and easily installed about slip segments 42.Slip wedge 48 is initially positioned in a slidable relationship to, andpartially underneath, slip segment 42. Slip wedge 48 is shown pinnedinto place by pins 50. Located below the upper slip wedge 48 is at leastone sealing element 36. The embodiment of FIG. 2 has a packer elementassembly 52 consisting of three expandable sealing, or packer elements36 disposed about mandrel 26. Packer shoes 56 are disposed at the upperand lower ends of packer element assembly 52 and provide axial supportthereto. The particular packer seal or element arrangement shown in FIG.2 is merely representative, as there are several packer elementarrangements known and used within the art.

Located below a lower slip wedge 48 are a plurality of slip segments 42.A mule shoe 58 is secured to mandrel 26 by radially oriented pins and/orepoxy glue 60. Mule shoe 58 extends below the lower end 30 of mandrel 26and has a lower end 62, which comprises lower end 13 of downhole tool10. The lowermost portion of downhole tool 10 need not be a mule shoe58, but could be any type of section, which serves to terminate thestructure of downhole tool 10, or serves as a connector for connectingdownhole tool 10 with other tools, a valve, tubing or other downholeequipment.

Referring back to FIG. 2, mandrel 26 has a recess 66 positioned at ornear lower end 30 thereof. Longitudinal central flow passage 32 hasfirst inner diameter 68 and second inner diameter 70 which definesrecess 66. Second inner diameter 70 is thus greater than first innerdiameter 68. Recess 66 also defines a shoulder 72. A solid plug 74 isremovably disposed in mandrel 26, preferably in recess 66. Plug 74 isdetachably connected to mandrel 26 with a shear pin 76 or otherretention method. Plug 74 has a receptacle 78 in an upper end 80thereof. Plug 74 has O-ring 82 to sealingly engage recess 66.

A rod 84 having upper end 86 and lower end 88 is disposed inlongitudinal central flow passage 32. Lower end 88 engages solid plug74, and is received in receptacle 78, making contact therewith. Upperend 86 extends beyond lower end 33 of ball seat 34 to space ball seat 34from sealing ball 35 and to prevent sealing ball 35 from prematurelyseating in ball seat 34. In an alternative embodiment, receptacle 78 isnot utilized, and rod 84 simply contacts upper end 80 of plug 74.

The operation of downhole tool 10 is as follows. Downhole tool 10 islowered into wellbore 12 with setting tool 22, which is a setting toolof a type known in the art. As downhole tool 10 is lowered into wellbore12, flow through longitudinal central flow passageway 32 will beprevented due to solid plug 74. Sealing ball 35 is positioned and spacedfrom ball seat 34 by rod 84. Once downhole tool 10 has been lowered to adesired position in well 14, setting tool 22 is utilized to movedownhole tool 10 from its unset position to the set position, asdepicted in FIGS. 2 and 3, respectively. A setting sleeve (not shown)will engage spacer ring 38, so that as setting tool 22 moves upwardly,spacer ring 38 is held in place. Once set, all upward and downward fluidcommunication from above and below plug 74 is prevented. Tool 10 thusacts as a bridge plug to prevent flow in the well. Tool 10 may be set inthe well above a previously perforated and fractured zone, for example,second zone 20 in FIG. 1. A zone thereabove, for example, first zone 18,may be fractured, and tool 10 a, acting as a bridge plug, prevents fluidfrom zone 20 from passing upwardly, and likewise prevents fluid pressurefrom above tool 10 a from acting on zone 20.

To convert downhole tool 10, plug 74 is removed from mandrel 26.Removing plug 74 requires the exertion of a predetermined pressure tocreate a sufficient force upon plug 74 to detach or remove plug 74. Inone embodiment, plug 74 is retained with shear pin 76 and thepredetermined pressure force will shear pin 76. The fluid pressurerequired to remove plug 74 will be less than the pressure used tofracture a zone thereabove, so that tool 10 automatically converts to afrac plug upon the fracturing of a zone thereabove. The shearing ofshear pin 76 allows plug 74 and rod 84 to fall through well 14. Upon thedetaching of plug 74, tool 10 performs as a standard frac plug wheresealing ball 35 seats and unseats from ball seat 34 according to thepressure of communicated fluid from above. Removing solid plug 74 andcontacting sealing ball 35 with ball seat 34 is simultaneous in thedescribed embodiment.

Using FIG. 1 for exemplary purposes, first tool 10 a may be lowered intowell 14 and set above formation 20, which will have been perforated andfractured prior to setting tool 10 a in well 14. Pressure may beincreased to fracture zone 18 thereabove. When initially set in well 14tool 10 will act as a bridge plug to prevent flow upwardly through thetool from formation 20. The fracture pressure will be greater than thatrequired to move or disconnect plug 74 from mandrel 26 in tool 10 a sothat the application of the fracturing pressure will automaticallyconvert tool 10 a into a frac plug. Conversion simply results from theincreased pressure which will act upon plug 74 to remove it therefromand simultaneously move sealing ball 35 into engagement with seat 34.Fracturing thus continues in the normal manner. Once zone 18 has beenfractured, pressure may be relieved and fluid from zones 20 and 18 maypass upwardly to the surface. Thus, tool 10 a acts simply as a fracplug. If desired, the process may be repeated such that a second toolreferred to in FIG. 1 as tool 10 b may be set in the well above zone 18and the process described herein repeated. The process can be repeatedas many times as desired in a well. Thus, as described herein, the tool10 may be converted from a bridge plug to a frac plug while in the wellto effectively prevent communication from a lower zone into an upperzone and vice versa until fracturing is complete. The automaticconversion to the frac plug will allow all zones to communicate to thesurface once all fracturing has been completed.

Thus, it is seen that the apparatus and methods of the present inventionreadily achieve the ends and advantages mentioned as well as thoseinherent therein. While certain preferred embodiments of the inventionhave been illustrated and described for purposes of the presentdisclosure, numerous changes in the arrangement and construction ofparts and steps may be made by those skilled in the art, which changesare encompassed within the scope and spirit of the present invention asdefined by the appended claims.

1. A downhole tool for use in a well comprising: a mandrel defining acentral flow passage and a ball seat; a sealing element disposed aboutthe mandrel and movable from an unset to a set position in the well; aplug detachably disposed in the mandrel for completely preventing flowthrough the central flow passage; and a sealing ball longitudinallyspaced from the ball seat, wherein application of a predeterminedpressure in the well will detach the plug from the mandrel and move thesealing ball into engagement with the ball seat.
 2. The downhole tool ofclaim 1, further comprising a rod disposed in the mandrel, wherein therod engages the sealing ball to space the sealing ball from the ballseat until the plug is detached.
 3. The downhole tool of claim 1, theplug having a rod extending therefrom to engage the sealing ball andspace the sealing ball from the ball seat.
 4. The downhole tool of claim1, wherein the tool comprises a bridge plug prior to detachment of theplug from the mandrel, and a frac plug after detachment.
 5. A downholetool for use in a well, the tool comprising: a mandrel having an upperand a lower end, the mandrel defining a longitudinal central flowpassage therethrough, wherein the mandrel defines a ball seat on theupper end thereof; a sealing element disposed about the mandrel forsealingly engaging the well; a plug detachably retained in the mandrel;and a rod disposed in the longitudinal central flow passage, the rodhaving first and second ends, the first end contacting the plug andextending therefrom in the longitudinal flow passage.
 6. The downholetool of claim 5, further comprising a sealing ball spaced apart from theball seat.
 7. The downhole tool of claim 6, wherein a second end of therod engages the sealing ball to space the sealing ball from the ballseat and to prevent the sealing ball from engaging the ball seat until apressure of a predetermined amount is applied in the well.
 8. Thedownhole tool of claim 7, wherein the predetermined pressure issufficient to detach the plug from the mandrel.
 9. The downhole tool ofclaim 7, wherein the plug is detached and removed from the mandrel andthe ball moved into engagement with the ball seat upon the applicationof the predetermined pressure in the well.
 10. The downhole tool ofclaim 7, wherein the tool converts from a bridge plug to a frac plug inthe well upon detachment of the plug from the mandrel.
 11. The downholetool of claim 5, wherein the downhole tool is movable from an unset to aset position in the well.
 12. A method for converting a downhole toolfrom a bridge plug to a frac plug comprising: lowering the downhole toolinto the well, the downhole tool defining a longitudinal central flowpassage therethrough; blocking flow in both an upward and a downwarddirection through the longitudinal central flow passage with a solidplug disposed therein; setting the downhole tool in the well so that thedownhole tool sealingly engages the well; positioning a sealing ball inthe well above the longitudinal central flow passage; increasing apressure in the well to a predetermined pressure to remove the solidplug; and contacting a ball seat on the downhole tool with the sealingball, the sealing ball preventing flow in the downward direction throughthe longitudinal central flow passage.
 13. The method of claim 12,further comprising the step of perforating the well above the tool priorto the step of increasing the pressure in the well to the predeterminedpressure.
 14. The method of claim 12, further comprising the step offracturing a zone above the tool after the step of contacting the ballseat with the sealing ball.
 15. The method of claim 12, furthercomprising spacing the ball from the ball seat with a rod that engagesthe solid plug.
 16. A method of fracturing a plurality of zones in awell comprising: (a) fracturing a first zone in the well; (b) lowering abridge plug into the well, the bridge plug comprising a mandrel with asealing element disposed thereabout and a solid plug disposed therein,the mandrel defining a longitudinal flow passage therethrough; (c)placing a sealing ball in the well prior to setting the bridge plug inthe well; (d) spacing the sealing ball from the longitudinal flowpassage; (e) setting the bridge plug in the well above the firstfractured zone; (f) simultaneously detaching the solid plug and movingthe sealing ball into engagement with the ball seat to convert thebridge plug to a frac plug; and (g) fracturing a second zone above thetool.
 17. The method of claim 16, where the simultaneous detaching andmoving step comprises increasing pressure in the well above the bridgeplug.
 18. The method of claim 16, further comprising decreasing pressurein the well to allow fluid from the first zone to pass upwardly throughthe longitudinal flow passage.
 19. The method of claim 16, furthercomprising: repeating steps (a)-(e) above the second fractured zone witha second bridge plug; simultaneously detaching the solid plug and movingthe sealing ball of the second bridge plug into engagement with the ballseat of the second bridge plug to convert the second bridge plug to asecond frac plug; and fracturing a third zone above the second fracplug.
 20. The method of claim 19, further comprising decreasing pressurein the well after fracturing the third zone so that fluid from thefirst, second and third fractured zones may pass upwardly in the well.21. A method of converting a downhole tool from a bridge plug to a fracplug in the well comprising: lowering a mandrel having an upper andlower end into the well, the mandrel defining a longitudinal centralflow passage therethrough and a ball seat on the upper end thereof, themandrel having a solid plug connected therein for blocking flowtherethrough; positioning a frac ball in the well spaced from the ballseat; and simultaneously detaching the solid plug from the mandrel andmoving the sealing ball into engagement with the seat, so that flowdownwardly through the longitudinal central passage is prevented andupward flow therethrough is allowed.
 22. The method of claim 21, furthercomprising: positioning a rod in the longitudinal flow passage; andspacing the sealing ball from the seat with the rod prior to detachingthe plug from the mandrel.
 23. The mandrel of claim 22, wherein the rodengages the solid plug and the sealing ball.